Hob cutter and method of making same



Oct. 27,v 1931. c OLSON 1,829,292

HOB CUTTER AND METHOD OF MAKING SAME Filed May 5, 1929 2 Sheets-Sheet l Oct. 27, 1931. c, G OLSON 1,829,292

HOB CUTTER AND METHOD OF MAKING SAME Filed May 3, 1929 2 Sheets-Sheet 2 fizz/622207",-

Patented @ct. 27, 1931 PATENT Frie CARL G. OLSON, OF CHICAGO, ILLINOIS, ASSIGNOR TC ILLINOIS TOOL WGRKS, CF CHICAGO, ILLINOIS, A COREORATION OF ILLINOIS HOB CUTTER AND METHOD OF MAKING SAME Application filed May 3,

My invention relates to rotary cutters having relieved teeth and to methods of making them, but more particularly to hobs and to methods of relieving the teeth thereof.

One of the primary objects of my present invention is to provide a hob which is so constructed that the surfaces of the teeth thereof may be ground by the use of a wheel of relatively large diameter and to this end I propose to preliminarily relieve the hob teeth so as to present a compound tooth construction.

More specifically itis an object of my present invention to provide a rotary cutter as set forth above in which the forward portion of each tooth may be initially round without carrying the grinding wheel into contact 1 with the rearward portion thereof, whereby merge or blend with the rearward portions.

grinding wheels of relatively large diameter may be employed without the necessity of mcreasing the. Width of the hob gashes.

Another object of my present invention is to provide a' hob cutter having peripheral teeth which are relieved in such a manner as to make for longevity and to render the hob eflicien'tly operable.

Still another object of my invention is to initially provide the cutter teeth with a compound relief of such a'nature that the rearward portion as 'well as the forward portion of each tooth may be used for hobbing purposes and thatsaid rearward ortion will serve also to lend strength an rigidity to the forward portion.

To accomplish these and other objects I propose to practice a tooth relieving method whereby a compound movement is lmparted to the relief cutting'tool so as to produce forward and rearward relieved tooth portions which are both eccentrically relieved, and then grind the surface of the forward portions of the teeth until said forward portions These and numerous other objects will be more apparent from the following detailed description when considered in connection with the accompanying drawings, wherein:

Figure 1 is an end elevational view of a rotary cutter or hob which is representative of one embodiment of my invention;

1929. Serial n 360,136.

Figure 2 is a fragmentary elevational view of the cutter as viewed from the right of Figure 1;

Figure 3 is an end elevational view similar to Figure 1 disclosing the hob after the forward portions of the teeth have been ground by means of the grinding wheel which is disclosed in association therewith;

Figure 4 is a fragmentary elevational view of the hob as viewed from the right of Fig- 00 ure 3;

Figure 5 is an end elevational view of the hob after the forward portions or sections of each of the teeth have been ground away as the result of sharpening, said view disclosing the manner in which the grinding wheel may then be applied to that portion of each tooth which originally was the rearward and supporting portion;

Figure 6 is a fragmentary elevational view as viewed from the right of Figure 5;

Figure 7 is an end elevational view of a thread milling, hob constructed in accordance with the teachings of my present invention,

the same being shown in association with a with my 8 Referring now to the drawings more in detail wherein like numerals have been em ployed to designate similar parts throughout the various figures, it will be observed that one form of rotary cutting tool which characterizes my present invention is the generating hob disclosed in Figures 1 to 6 inclusive which I have designated generally by the numeral 10. This hob comprises a cylindrical body portion 12 which is formed with a pluralit Y of peripheral teeth 14. In

preliminarily ormin these teeth 14, it is common practice to subsequently mill thetransverse gashes 16. After these gashes 16 have been formed, the

rst form a. helix and teeth are ready to be relieved and my present inventionrela'tes particularly to an improved teeth. The, rearward section 22 of each tooth method of relieving these teeth. lends considerable rigidity and support for Referrin particularly toFigures 1 and 2, the forward ground portion 18. The porit will be served that the forward portion tions of the teeth removed by grinding are i 5 or section of each tooth is designated by the indicated by the radial dot and dash .lines numeral 18, the medial portion of each tooth shown in Figure 3 and when the faces of the by the numeral 20 and the re rward section teeth have been ground back so as to remove by the numeral 22. The relief formed in all the stock included within the section desthese teeth 14 is of a compound nature. In ignated by these dot and dash lines, the unother words, when the forming or relieving ground portions 22 of the teeth will be "tool is applied to a tooth, said tool is first reached. If it is deemed desirable, these pormoved along a path embraced by the fortions 22 may now be ground in the manner ward tooth section 18 and when said tool disclosed in Figure 5. Obviously, the sec- ,reaches the medial portion of the tooth, a tions 22 of the teeth not only serve as a supforward movement is imparted to the tool so port and strengthening medium for the comas to present the mid-section 20. From this panion' forward portions, but. may also be oint the tool 'is'moved along1 a path em'- used for actual hobbing purposes. While obraced by the rearward toot section 22, viously, the strength. of the hob teeth is rewhich path has the same, degree of eccenduced-after the same have assumed the size tricity as that embraced by the forward tooth disclosed in Figure 5, said teeth have sulfisection 18, as shown by the dot and dash lines cient strength to be used for certain practical in Figure 1. Thus, it mi ht 'be stated that purposes. It will thus be apparent that by in practicing my improve method of relievpracticing my improved method of tooth reing the hob teeth, an ordinary degree of relieving, so as to provide the forward and 25 lief is applied to the forward section 18, a rearward tooth sections with different relief eater relief at the intermediate ortion 20 characteristics having the same degree of ecand then the ordinary degree 0 relief is centricity, the utility of the hob is materialagain applied to the rearward portion. The 1y increased by reason of the fact that the center about which the relieving tool gnot rearward supporting, sections 22 may be used shown) moves is indicated'by the numera 23. for actual gear cutting purposes.

After the hob teethhave been relieved in My invention is particularly adaptable in the manner just described, a grinding wheel forming the relief on hob milling cutters of 24 is applied so as to grind the forward porthe type disclosed in Figures 7 and 8, said tion or section 18 of each tooth, said wheel becutter being indicated generally by the nuing moved about the eccentric axis 23. This meral 28. A thread milling cutter is repregrinding wheel may be a plied to said forsentative of one of those types of cutters ward toothriportions wit out engaging the which require the teeth to be ground with rearward portions.- Hence, the grinding comparatively large grinding wheels in wheel 24 may be of considerably greater order-to obtain sharp tooth corners. The

40 diameter than the wheel which would be usual method of making thread milling cut-' employed if the entire peripheral surfaceof ters is to provide the cutter with exceptionthe teeth were to be ground. @tock is really wide 'flutes in order to make room for moved from the forward ortions 18 of the the grinding wheel to run out at the rear teeth b said grinding w eel until the surend of the teeth-without striking the cutting faceso said forward portions blend or merge edges of the following row of teeth. This with the unground surface portions of the makes the hob teeth comparatively short and rearward tooth sections. 22'. ?After the for hence the usable portion of the teeth is still ward ground sections of the tooth merge with shorter in view of the fact that the rear porthe unground rearward sections 22, the hob tion of each tooth must be left for supportteeth will assume the conventional form dising the cutting edge. By practicing my imclosed in Figure 3. That is to say, the ground proved. method, the hob 28 is provided with front part of each tooth and the unground a plurality of peripheral teeth 14-11 which rear part of each tooth will have 'the same are formed with a compound relief similar final relief.- The advantage of having the to that just described in connection with the rearward portions 22 relieved with the same hob 10. Thus the teeth 14= a"are initially 1 degree of eccentricity as the forward porrelieved was to present a forward portion tions 18 will be more apparent when the or section 18 a having the usual degree of sharpening operation of the hob teeth is conrelief, amedlal section 20-11 of reater relief sidered. T and a rearward section 22a w ich is of the m In sharpening hob teeth it is customary same degree of eccentricity as the forward to employ a 'nding wheel 26 shown fragportlon 18-a. It w1ll thus be apparent that mentarily in igure 3, which 'ndin wheel after the teeth 14-a /have been initially enga es the front faces of the ob teet Obformed with the above; mentioned relief, a vious y, each sharpening st ke -past the grinding wheel 24-a. may be employed to a wheel 26 remoyes stock from e face of the grindaway the forward tooth portions 18 a and hence the true profile of in the 'manner described in connection with the grinding of the forward portions 18 of the hob teeth 14. It will also be apparent that a grinding wheel of relatively large diameter may be employed without the necessity of increasing the size of the hob gashes. After the teeth in the cutter 28 have been re peatedly sharpened so as to grind away the entire forward portions of the teeth, the rearward portion still remains and this rearward portion may be put into actual service for hobbing operations. If it is desired, this remaining rearward portion may also be ground by use of the grinding wheel 24a.

From the foregoing it will be apparent that my invention contemplates the provision of a hob having improved structural tooth characteristics and said invention also contemplates the provision of an improved simple method of relieving teeth in hobs or rotary cutters of like nature which will increase the longevity of the cutter. In other words, the entire structure of each tooth in the cutter may be employed for actual cutting purposes. That is to say, the rearward as well as the forward portions of each toothmay be used for hobbing purposes and not only as a means for lending rigidity to the forward tooth portions. .By practicing the described method of tooth relieving, the degrees of eccentricity in the forward and rearward portions of the teeth are the same the entire tooth structure is maintained.

While I have described my invention in connection with particular types of rotary cutters, namely, specific forms of hobs, it is to be understood that the invention is capable I d of application to many other forms of rotary cutters having relieved teet Having thus described my invention, what I claim as new and desire to secure by Letters Patent is: I

1. In a rotary cutter of the class described, a body portion, and a plurality of relieved cutting teeth thereon, the forward peripheral surface of each tooth being ground and the rearward portion of each tooth being un-' ground, said unground rearward portion having the same degree of eccentricity as the forward ground portion, the thickness of the ground portion being greater than the thick: ness of the unground portion.

2. In a rotary cutter of the class described, a body portion, and a plurality of relieved teeth provided thereon, said teeth having a forward peripheral ground portion and a rearward peripheral unground portion, the thickness of the ground portion being greater than the thickness of the. unground portion, said rearward unground portion having the same degree of eccentricity as the forward ground portion and being of such a size as to lend rigidity to the forward ground portion.

3. In a rotary cutter of the class described,

the teeth to be tion having a greater relief than said for ward portion and the rearward portion hav-. ing a relief which is less than the medial portion, whereby said forward peripheral portion may be conveniently ground.

4. In a rotary cutter of the class described, a body portion, and a plurality of relieved teeth provided thereon, said teeth having a forward peripheral portion having a given eccentricity, a medial portion having a different eccentricity and a rearward portion having the same eccentricity as the forward portion, whereby said forward portion may be conveniently ground, the forward portion being larger than the rearward portion.

5. In a rotary cutter of the class described, a body portion, and a plurality of relieved cutting teeth provided thereon positioned between transverse flutes, the forward peripheral surface of each tooth having a given eccentricity and the rearward peripheral surface of each of said teeth having the same degree of eccentricity but positioned with respect to the forward peripheral surface so as to permit said forward peripheral surfaces of ground without grinding said rearward tooth surfaces.

6. The method of relieving cutter teeth whichconsists in rotating the cutter, applying a cutting tool to the teeth and causing relative movement between the cutter and the tool so as to cause the forward peripheral portions of a tooth to be relieved with a given egree of eccentricity, radially shifting the relative positions of the cutter and tool and then imparting a relief to the rearward portion of the tooth which has substantially the same degree of eccentricity as the relief im-' parted to the forward portion of the tooth.

7. The method of relieving cutter teeth which consists in rotating the cutter, applying a forming tool to the peripheral surfaces of the cutter teeth, imparting relative movement between the tool and the'cutter so as to relieve the forward portion of a cutter tooth with a given degree of eccentricity, imparting an increase in relief to the medial portion of said tooth and then relieving the rearward portion thereof with the same degree of eccentricity as the forward portion.

8. The method of relieving cutter teeth which consists in rotating the cutter, applying a forming tool to the peripheral surfaces of the cutter teeth, imparting relative movement between the tool and the cutter so as to relieve the forward portion of a cutter tooth with a given degree of eccentricity, imparting an increase in relief to the medial portion of said tooth, imparting a relief to the rearward portion of the tooth, and then grinding the forward peripheral surface of the tooth until ment 4 I 13mm ,said surface blends the rearward surface.

-9. The method 'of'relieving cutter teeth which -consists in rotating the cutter, applying a forming tool to the peripheral surfaces of the utter teeth, imparting relative movebiatween the tool and the cutter so as to relieve the forward portion of the cutter teeth with a given de ee of eccentricity, imparting a relief to ti e rearward portion of the tooth which is of substantially the same eccentricity as the forwardportion but which I is radiall shifted with res ect to said forward sur ace, and then grin 'ng the forward peripheral surface of each tooth until said surface blends with the rearward 'unground portion.

10. In arotary cutter of the class described, a body portion, and a plurality of relievedl cutting teeth thereon, the forward peripheral relieved-surfaces of each tooth constituting the largest diameter range and ground onthe sides to present a true involute helicoidal surface, succeeding diameter ranges of each tooth being unground, said unground portions having the same degree of eccentrlcity as the forward peripheral surfaces.

In witness-whereof, I have hereuntosubscribed my name.

' CARL G. OLSON. 

